Serotonin (5-hydroxytryptamine, 5-HT) is a biogenic monoamine which plays a prominent role in a variety of physiological functions in both the central nervous system (CNS) and the periphery of the body. These pleiotropic effects are mediated by at least 14 different receptors which are grouped into seven families (5-HT1-7) according to their primary structure and their intracellular signal transduction coupling systems (Hoyer, D., et al., Pharmacol Biochem Behav, 2002. 71(4): p. 533-54). With the exception of the 5-HT3 receptor, which is an ion channel, all serotonin receptors are G-protein coupled receptors (GPCRs).
The 5-HT2 receptor family consists of 5-HT2A, 5-HT2B, and 5-HT2C receptors. A number of studies suggest that the 5-HT2C receptor system is specifically involved in diseases or conditions such as the metabolic syndrome including obesity, type II diabetes, and dyslipidemia, as well as CNS-related disorders including depression, schizophrenia, obsessive-compulsive disorder, drug abuse, sleep disorders, anxiety and epilepsy.
Obesity is a life-threatening disorder in which there is an increased risk of morbidity and mortality arising from concomitant diseases such as, but not limited to, type II diabetes, hypertension, stroke, certain forms of cancers and gallbladder disease. Obesity has become a major healthcare issue in the Western World and increasingly in some third world countries. The increase in the number of obese people is due largely to the increasing preference for high fat content foods but also, and this can be a more important factor, the decrease in activity in most people's lives. In the last 10 years there has been a 30% increase in the incidence of obesity in the USA and that about 30% of the population of the USA is now considered obese. In spite of the growing awareness of the health concerns linked to obesity the percentage of individuals that are overweight or obese continue to increase. In fact, the percentage of children and adolescents who are defined as overweight has more than doubled since the early 1970s and about 13 percent of children and adolescents are now seriously overweight. The most significant concern, from a public health perspective, is that children who are overweight grow up to be overweight or obese adults, and accordingly are at greater risk for major health problems. Therefore, it appears that the number of individuals that are overweight or obese will continue to increase. Whether someone is classified as overweight or obese is generally determined on the basis of his or her body mass index (BMI) which is more highly correlated with body fat than any other indicator of height and weight. A person is considered overweight when they have a BMI in the range of 25-30 kg/m2, whereas a person with a BMI over 30 kg/m2 is classified as obese. Obesity is further divided into three classes, Class I (BMI of about 30 to about 34.9 kg/m2), Class II (BMI of about 35 to 39.9 kg/m2) and Class III (about 40 kg/m2 or greater). There are problems with this definition in that it does not take into account the proportion of body mass that is muscle in relation to fat (adipose tissue). To account for this, obesity can also be defined on the basis of body fat content: greater than 25% and 30% in males and females, respectively.
It has been recognized that obesity is a disease process influenced by environmental factors in which the traditional weight loss methods of dieting and exercise need to be supplemented by therapeutic products (S. Parker, “Obesity: Trends and Treatments”, Scrip Reports, PJB Publications Ltd, 1996). As the BMI increases there is an increased risk of death from a variety of causes that is independent of other risk factors. The most common diseases with obesity are cardiovascular disease (hypertension, coronary insufficiency, coronary heart disease, angina pectoris, congestive heart failure, atheromatous disease, cardiac insufficiency), high blood cholesterol, dyslipidemia, type II (non-insulin dependent) diabetes, insulin resistance, glucose intolerance, hyperinsulinemia, stroke, gall bladder disease (particularly gallstones and cancer), cholescystitis and cholelithiasis, gout, osteoarthritis, obstructive sleep apnea and respiratory problems, some types of cancer (such as endometrial, breast, prostate, and colon), complications of pregnancy, poor female reproductive health (such as menstrual irregularities, infertility, irregular ovulation), diseases of reproduction (such as sexual dysfunction, both male and female, including male erectile dysfunction), bladder control problems (such as stress incontinence), uric acid nephrolithiasis, psychological disorders (such as depression, eating disorders, distorted body image, and low self esteem). Research has shown that even a modest reduction in body weight can correspond to a significant reduction in the risk of developing coronary heart disease.
As the 5HT2C receptor is expressed in high density in the brain (notably in the limbic structures, extrapyramidal pathways, thalamus and hypothalamus i.e. PVN and DMH, and predominantly in the choroid plexus) and is expressed in low density or is absent in peripheral tissues, a selective 5HT2C receptor agonist can be an effective and safe pharmaceutical agent. Also, 5HT2C knockout mice are overweight with cognitive impairment and susceptibility to seizure thus establishing the clear use for a 5HT2C receptor agonist in 5HT2C receptor associated diseases or disorders. The 5HT2C receptor plays a role in obsessive compulsive disorder, some forms of depression, and epilepsy. Accordingly, 5HT2C receptor agonists can have anti-panic properties, and properties useful for the treatment of sexual dysfunction. In addition, 5HT2C receptor agonists are useful for the treatment of psychiatric symptoms and behaviors in individuals with eating disorders such as, but not limited to, anorexia nervosa and bulimia nervosa. Individuals with anorexia nervosa often demonstrate social isolation. Anorexic individuals often present symptoms of being depressed, anxious, obsession, perfectionistic traits, and rigid cognitive styles as well as sexual disinterest. Other eating disorders include, anorexia nervosa, bulimia nervosa, binge eating disorder (compulsive eating) and ED-NOS (i.e., eating disorders not otherwise specified-an official diagnosis). An individual diagnosed with ED-NOS possess atypical eating disorders including situations in which the individual meets all but a few of the criteria for a particular diagnosis. What the individual is doing with regard to food and weight is neither normal nor healthy.
The first line of treatment for individuals that are overweight or obese is to offer diet and life style advice, such as, reducing the fat content of their diet and increasing their physical activity. However many patients find these difficult to maintain and need additional help from drug therapy to sustain results from these efforts.
Compounds marketed as anti-obesity agents include Orlistat and Sibutramine. Orlistat (a lipase inhibitor) inhibits fat absorption directly and tends to produce a high incidence of unpleasant (though relatively harmless) side-effects such as diarrhea. Sibutramine (a mixed 5-HT/noradrenalin reuptake inhibitor) can increase blood pressure and heart rate in some patients. The serotonin releaser/reuptake inhibitors fenfluramine and dexfenfluramine have been reported to decrease food intake and body weight over a prolonged period (greater than 6 months). However, both products were withdrawn after reports of preliminary evidence of heart valve abnormalities associated with their use. There is therefore a need for the development of a safer anti-obesity agent.
The compounds of formula (I) are useful in the treatment and/or prevention of disorders involving elevated plasma blood glucose, particularly diabetes mellitus (including Type II or non-insulin dependent diabetes mellitus (NIDDM); Type I or insulin dependent diabetes mellitus (IDDM); and Type III or malnutrition-related diabetes). The diabetes maybe diabetes secondary to pancreatic disease; or diabetes related to steroid use. The compounds of formula (I) are also useful in the treatment and/or prevention of the sequelae of hyperglycemia; in the treatment and/or prevention of diabetic complications; and in the treatment of insulin dependence. The invention is of particular use in the treatment or prevention of diabetes mellitus (including Type II or non-insulin dependent diabetes mellitus (NIDDM); Type I or insulin dependent diabetes mellitus (IDDM); and Type III or malnutrition-related diabetes), and particularly in the treatment or prevention of Type II diabetes.
Diabetes has also been implicated in the development of severe sequelae such as kidney disease, eye diseases and nervous-system problems. Kidney disease, also called nephropathy, occurs when the kidney's “filter mechanism” is damaged and protein leaks into urine in excessive amounts and eventually the kidney fails. Diabetes is also a leading cause of damage to the retina and increases the risk of cataracts and glaucoma Finally, diabetes is associated with nerve damage, especially in the legs and feet, which interferes with the ability to sense pain and contributes to serious infections. Taken together, diabetes complications are one of the leading causes of death.